The purpose of this proposal is to develop and qualify a continuous, miniature, atraumatic fiberoptic intravenous sensor and display system. The most common use of magnesium therapy is obstetrics where the infusion rate of MgSO4 is regulated by clinical signs. The instantaneous regulation of MgSO4 infusion will be safer and more effective with immediate feedback on the blood magnesium. A small, inexpensive, disposable and continuously monitoring Mg2+ sensor would be cost effective, providing vital and immediate diagnostic and clinical feedback. The specific aims of Phase I are: 1. Develop a Mg2+ complexing dye system with suitable characteristics. 2. Design a Mg2+ fiber optic sensor and evaluate its performance. 3. Evaluate practicality of instrumentation and calibration of the sensor. The longer term Phase II work will include: 1. Finalize the sensor design, calibration and instrumentation. 2. Develop manufacturing methods for high volume production.